1. Field of the Invention
The present invention relates to a high-alumina refractory for use in a furnace for melting non-ferrous metals having a melting point not higher than 1200.degree. C., more particularly to a refractory suitable for use in a furnace for melting copper alloys.
2. Description of the Prior Art
High-alumina refractory is used for example as inner lining in a furnace for melting copper, brass, zinc, aluminum, or other non-ferrous metals. This high-alumina refractory comprises particles of high-alumina aggregate, in which aluminum oxide accounts for at least 60% by weight, the balance being substantially silicon dioxide, and a binding agent.
This high-alumina refractory, however, has disadvantages of being poor in resistance to thermal shock and forming a reaction product in contact with an aluminum melt. Because of the poor resistance to thermal shock, the inside of a copper- or copper alloy-melting furnace in which said refractory is applied is susceptible to cracks when the furnace is cooled. When the furnace is again used for melting copper or copper alloys, the melt penetrates into the furnace walls through these cracks, which causes peeling of the inside wall portions in which the melt has penetrated on account of the difference in the thermal expansion coefficient between the portions in which the melt has penetrated and those in which it has not penetrated when the furnace is cooled. There is a danger of coil shortcircuiting accidents caused by the penetration of the copper melt in an induction melting furnace.
When aluminum or aluminum alloys are molten in a furnace wherein said refractory is applied, the melt reacts with the refractory to form a reaction product, which adheres to the furnace walls resulting in the decrease in the internal area of the furnace. Moreover, some of the components of the aluminum alloy melt causes part of the reaction product to penetrate into the inside of the furnace, thus bringing about the peeling of the walls.
The present inventor has previously discovered that the resistance to thermal shock of the high-alumina refractory can be improved and the reaction with aluminum melt can be prevented by incorporating silicon nitride in the refractory (see, for example, Jap. Laying-open No. 56-22675).